1. Field of the Invention
The present invention relates to the management of optical networks arranged in a ring-configuration, and in particular to a method of managing the traffic protection in OMS-SPRING ring networks, wherein the change of allocation of the wavelengths in the traffic transit nodes is provided.
2. Description of the Prior Art
In the OMS-SPRING ring optical networks (Optical Multiplex Section-Shared Protection Ring), a shared protection mechanism is implementable which allows the automatic restoration of traffic in the presence of interchange causes (defects or failures in the connection fibers and/or in the optical elements which operate for the elaboration of the multiplexed optical signal). The OMS-SPRING networks can implement the automatic restoration of traffic through the synchronized re-routing of said traffic, which is possibly activated by each node of the configurated ring, and to be considered as a part of the protection scheme owing to the interchange reasons detected by the node itself. This operation is implementable through a protocol consisting of messages continuously interchanged between adjacent nodes.
In order to illustrate the present invention and the state of the art, it is considered as convenient to give a series of considerations and definitions.
In the optical networks are defined working wavelengths (λWK), utilized for carrying high priority traffic (Normal Traffic, NT), and protecting wavelengths (λPR) utilized for carrying the low priority traffic (Extra Traffic, ET). In each network element forming the optical ring network connection matrices are present. The following re-configuration actions of connection matrices are defined, which matrices are present in the nodes of the ring network, wherein the OMS-SPRING scheme is configurated:                “bridge”, namely an action by which the data flow inserted in the generic working wavelength is inserted into the corresponding protecting wavelength through the contemporary insertion into both the wavelengths or through the selection of the only protecting wavelength.        “switch”, namely an action by which the data flow is selected no more by the working wavelength, but by the corresponding protecting wavelength.        
Furthermore, in connection with the implementation field of the above said actions, the following protection processes are defined:                “span switch”: a protection process which is operated due to interchange reasons (failures or commands) detected at Optical Multiplex Section level in the fiber span which connects two of the nodes of the ring network under examination, and which causes the loss of only the high priority traffic carried on that span, that is makes the only working resource associated to that span unavailable. The span switch consists in the “bridge & switch” (BR&SW) action implemented in the nodes at the ends of the span affected by interchange cause, by exploiting the protecting resource which is available in the span itself.        “ring switch near end”: a protection process which is operated due to interchange reasons (failures or commands) detected at Optical Multiplex Section level in the span which connects two of the nodes of the ring network under examination, and which causes the loss both of NT traffic and of ET traffic carried on that span, that is makes both the working and protecting resources associated to that span unavailable. The ring switch near end consists in the BR&SW action implemented in the nodes at the ends of the span affected by interchange cause, by exploiting the alternative path of the ring network which connects the two nodes implementing the action.        “ring switch far end”: protection process which is operated due to interchange reasons (failures or commands) detected at Optical Multiplex Section level in the span connecting two of the nodes of the ring network under examination, and which causes the loss of both the NT traffic and the ET traffic carried onto that span, that is makes both the working and protecting resources associated to that span unavailable. The ring switch far end consists in the BR&SW action implemented in the termination nodes (add/drop) of high priority traffic carried in the span affected by the interchange cause, by exploiting the alternative path of the ring network which connects the two nodes implementing the action.        
All the above said protection processes are of the “dual ended” type, that is with appropriate synchronization of the bridge and switch actions which are obtainable through a signaling protocol operating between the nodes of the network wherein the OMS-SPRING protection scheme is configurated, and through which the nodes adjacent to the span affected by an interchange cause (both span and ring), which nodes could be defined as “switching nodes”, are signaling reciprocally the reason and the performed actions.
The aim of the present invention is not to define the syntax and the structure of the signaling protocol to be utilized for the management of the above mentioned protection processes (span switch, near end ring switch, far end ring switch), nevertheless, it is assumed that—whichever be the protocol utilized—at least the following information are to be interchanged between the nodes belonging to the protection scheme: Reason of the request, Source Node, Destination Node, Direction of Communication, Status of Protection. In particular:                “Reason of the request” indicates by an appropriate code—depending on a possible priority logic of the events—the type of failure;        “Source Node” indicates, by an appropriate code the ID of the node which generates the signaling;        “Destination Node” indicates, by an appropriate code, the ID of the node to which the signaling generated by the “Source Node” is addressed;        “Direction of Communication” indicates, by an appropriate code, the path which the signaling generated by the generic node is following to reach the adjacent node. It is possible to distinguish a “short” path, if the communication between both the nodes occurs directly through the connection span between them, from a “long” path when the communication between both the generic nodes can not occur through the connection span (because of failures) and therefore utilizes the remaining spans of the same ring;        “Status of protection” indicates, by an appropriate code, the re-configuration state of connection matrices, by distinguishing in principle among the following conditions:        No action, after the identification of an interchange cause and the beginning or modification of a protection process, namely, in general, when neither the “Bridge”, nor the “Switch” actions are in progress (that is no modification of the re-connection matrices).        Bridge and Switch, after the reciprocal reception, by the switching nodes, of the signaling containing the “Status of protection” which indicates “no action”.        
Then, suppose in the specific case of ring switch (near end or far end), that the BR&SW actions can be implemented by the involved nodes, if the cause of the request is a failure classified at high priority (for example the break of a fiber and/or of a component) and the Status of protection indicates that no action has been implemented with the aim of optimizing the operation time of the protection mechanism and of limiting the traffic loss.
In addition, assume that—in the absence of interchange requests—the signaling is nevertheless generated by the generic node configurated by the OMS-SPRING scheme towards the adjacent node. For this purpose, in order to verify the matching of the received signals, it is necessary that each node of the ring receives, together with the configuration data, the information about the ring topology (or “ring map”), wherein the nodes forming the network are indicated with the relevant ID, as well as their position.
The OMS-SPRING ring networks can foresee a mechanism named “Wavelength Interchange”, shortly WLI. By WLI it is indicated the configuration of a data traffic in a given ring network by allowing to such a traffic, which is carried in the n-th wavelength of OMS, to pass through a network element which is able to elaborate the protocol utilized for signaling, occupying numbers of λ which are different at the input and the output. If, for instance, the maximum capacity of a ring is of n λ, the WLI mechanism allows to enter a network element (a node of pure transit and wherein no termination of the signal carried by the wavelength is performed) with λ#X at its West (W) side and to go out from the East (E) side with a λ#Y, with X≠Y=1, 2 . . . , n. The advantage is a higher flexibility in the traffic allocation on the line resources and, therefore, an efficient band exploitation.
The protection process defined as span switch shows no implications which are relevant to the WLI mechanism: the span switch is managed within the span itself by both the end nodes. The possible allocation of traffic to be protected (in the adjacent spans) in a wavelength which is different from the one utilized in the span affected by an interchange cause, represents an outer function vis-à-vis the protection function and clearly has no influence on the protection process.
Nevertheless, more in general, the state of the art does not teach and nor suggest a mechanism for managing all the protection processes in an OMS-SPRING ring network, wherein the generic data flow—allocated on the high priority wavelength and subjected to protection—has been allocated on wavelengths which are different at the input and output of a generic node of the ring network which elaborates the signaling protocol utilized by the protection scheme.